Rotary variable resistor with oblique taps and brush spanning plural taps

ABSTRACT

A variable resistance element is provided in which a multicontact brush is slidable over a plurality of spaced tap terminals of a resistance element. The resistance element includes a resistance film deposited on a suitable backing and a deposited conductive film in spaced strip form forming extending tap terminals for the resistance film. The brush contacts are aligned transversely to the path of travel of the brush while the tap terminals are angularly disposed relative to the path of brush travel so that at least two tap terminals are engaged by the brush contacts as the contact brush is moved relative to the tap terminals.

United States Patent Fu ii et a1.

ROTARY VARIABLE RESISTOR WITH OBLIQUE TAPS AND BRUSH SPANNING PLURAL TAPS Talsuo Fujli; Yutaka Watano, both of Tokyo, Japan inventors:

Nippon Kogaku K. K., Tokyo, Japan Nov. 25, 1970 Assignee:

Filed:

Appl. No.:

Related US. Application Data Continuation of Ser. No. 768,721, Oct. 18, 1968, abandoned.

US. Cl ..338/190, 338/140 Int. Cl ..l-101c 9/04 Field oiSearch ..338/1l8,138-140,

[ Feb. 1, 1972 1 References Cited UNITED STATES PATENTS 3,161,850 12/1964 Klug 338/195 541,136 6/1895 Willms .338/140 Primary ExaminerLewis l-l. Myers Assistant Examiner-Gerald P. Tolin [57] ABSTRACT A variable resistance element is provided in which a multicontact brush is slidable over a plurality of spaced tap terminals of a resistance element. The resistance element includes a resistance film deposited on a suitable backing and a deposited conductive film in spaced strip form forming extending tap terminals for the resistance film. The brush contacts are aligned transversely to the path of travel of the brush while the tap terminals are angularly disposed relative to the path of brush travel so that at least two tap terminals are engaged by the brush contacts as the contact brush is moved relative to the tap terminals.

3 Claims, 7 Drawing Figures PATENIED FEB uszz 36391381 sum 2 or z .fi r' FIGA 8 I A L r' 7/ FIGS 8 PIC-3.6 8

FIG? {8 A A A ROTARY VARIABLE RESISTOR WITH OBLIQUE TAPS AND BRUSH SPANNING PLURAL TAPS This application is a continuation of Ser. No. 768,721, filed /18/68, now abandoned.

This invention relates to a variable resistance element, and more particularly to a resistance element of a deposited film of resistive material having tap electrodes of a deposited film of conductive material connected to the first film to provide small stepwise changes in the resistance value of the element as a contact brush is moved over the tap electrodes.

In the prior art, the variable resistance elements were subject to deterioration and wear of the contacts and electrodes, resulting in temporary variations in the resistance value as the sliding contact was moved over the tap electrodes. As will hereinafter appear, with wear of the tap terminals of the resistance element, or the wear of the sliding contact, the sliding contact would either not engage a tap electrode firmly, or instead of bridging two or three electrodes, the sliding contact would only engage one of the electrodes; or in the case of three electrodes, would engage only the outer two electrodes.

The object of the present invention is to provide a thin film, variable resistance element wherein a multicontact brush is provided to engage at least two of the tap terminals of the element as the brush is moved relative to the tap electrodes.

The present invention will be described in detail in connection with the accompanying drawings in which one possible embodiment of the invention is illustrated, in which FIG. 1 is a plan view of the resistance element embodying the invention, with the resistance film layer in cross section to illustrate the interconnection of the resistance layer and the tapelectrode film;

FIG. 2 is an enlarged plan view of the contact brush;

FIG. 2A is a side elevational view of FIG. 2; while FIGS. 3 through '7 are side views of tap electrodes and sliding contacts of conventional variable resistors illustrating the deterioration of these elements due to frictional wear.

By way of explanation, reference is first made to FIGS. 3 through 7 of the drawings illustrating the sliding contact and tap electrodes of a conventional variable resistor. Deposited or otherwise secured to a baseplate 10 are tap electrodes 9 which are connected to a resistance element (not shown), the tap electrodes being adapted to be engaged by a sliding contact 8. The width of the contact 8 is such that initially the contact 8 will engage at least two adjacent tap electrodes 9 as illustrated in FIG. 3. With use, the contacting surfaces of the electrodes 9 and contact 8 are worn away and the sectional shapes of the elements take the forms as illustrated in FIGS. 4 and 5. In FIG. 4, two of the tap electrodes 9 are bridged by the sliding contact 8. With additional wear, it will be noted that only one electrode is engaged by the contact, as illustrated in FIG. 5. In FIG. 6, an extreme example of contact and electrode erosion due to friction is illustrated, in this instance the dependent face of the contact engaging only the baseplate 10. In the case wherein a sliding contact engages more than three terminals, wear of the electrodes as illustrated in FIG. 7, could result in the contact only engaging three of the electrodes, the contact passing over one of the intervening electrodes. Thus with contact and electrode erosion it is likely that a sliding contact may move into a position wherein the circuit is opened (FIG. 6), or into positions which would normally provide a higher resistance value but in reality provide a reverse change in which the resistance value is lower than the preceding step, and vice versa.

The present invention overcomes these defects of the conventional variable resistance elements by providing a mu]- ticontact' sliding contact and film-deposited tap electrodes which are angularly disposed relative to the travel path of the sliding contact to provide a stepwise change in resistance value consistent with the degree and direction of contact movement.

Referring now to FIGS. 1 and 2 of the drawings, a circular baseplate 5 of suitable insulation material is provided on which is deposited by sputtering, printing, etching, vacuum depositing, or any other known method in the art, a film of low resistivity material to form comblike electrodes 2 of varying lengths and to provide a terminal electrode 4. Deposited on the film 2 is a second film of resistance material having a varying width and known resistance per unit area. It is to be noted from the drawing that those portions of the electrodes 2 (a through k) extending outwardlyof the resistance film 3 are inclined being chordal rather than radial relative to the circular baseplate 5. It will also be noted that the extreme outer edges of electrodes 4 and k are radial. In FIG. I, arcuate dashdot lines are used to illustrate the circular path of the sliding contact fingers 11 through 17 as illustrated in FIG. 2. The contacts are radially aligned relative to the circular baseplate and move in the arcs illustrated.

The sliding contacts 11 through 17 are carried at the ends of a plurality of spring fingers 6 secured in a retaining member 7 (FIG. 2) the contacts being bowed to provide a sliding surface 1 which engages-the electrodes with some pressure due to the spring fingers 6. The contact fingers 11 through 17 are connected in parallel and arranged in spaced, parallel relationship with the ,contact surfaces aligned; and adapted to span four electrodes and to engage at least two adjacent electrodes.

Referring to FIG. 1, the contact fingers 11 through I7 are in the position indicated by the arrow, the sliding surfaces 1 of the contact fingers being designated by the radial row of small circles. As previously indicated the contact fingers 11 through 17 are arranged to span four electrodes. Between contact fingers 11 through 17 there are the electrodes d, e, f and g. The electrodes and contact fingers are further arranged so that between any two electrodes there will be at least three consecutive contact fingers. In FIG. 1, contact fingers l1, l2, l3

and 14 span the electrodes d and e, and contact fingers l3, I4,

From the foregoing, it is apparent that as the contact fingers are moved relative to the tap electrodes, the contact fingers 11 through 17 will span four electrodes and engage at least three electrodes, two of the three engaged electrodes being adjacent electrodes. Thus in moving the contact brush counterclockwise from the right-hand position in FIG. 1, all seven brushes will engageterminal k. Contact finger 17 which may be considered the higher resistance finger, is the first to leave the electrode k to be followed by contact fingers I6, l5, l4, l3, l2 and then 11, the finger 11 being considered the lower resistance finger. The finger I7 is the first to contact the electrode j to be followed by the fingers 16 through 11. In the clockwise rotation of the brush assembly from terminal electrode 4, the contact finger 17 will leave the terminal first, followed by the other fingers and be the first to engage the successive tap terminals a, b, c, etc. Successive areas of the resistance film 3 are thus added or subtracted to provide a smooth variation in the resistance value of the element in small stepwise stages.

In forming the variable resistance element described, the resistance film 3 and the tap electrodes 2 and 4 could be deposited as a single layer instead of successive layers as described, or the electrodes 2 and 4 could be deposited over the resistance film 3. Preferably, the resistivity of the film forming the electrodes 2 and 4 is of lower resistivity than the resistance film 3 so that the resistance value of the tap electrodes may be ignored.

There is thus provided a variable resistance element in which the objectof this invention is achieved and which is well adapted to meet the conditions of practical use.

What we claim is:

1. A variable resistance element comprising a baseplate of insulating material,

a first resistance film of low resistivity material on said baseplate and forming comblike electrodes of varying lengths,

a second resistance film of varying width on said baseplate and electrically connected to the comblike electrodes formed by said first film, and

2. A variable resistance element according to claim 1,

. wherein the path of movement of the multicontact brush is arcuate.

3. A variable resistance element according to claim 1, wherein three consecutive contact fingers span two adjacent electrodes. 

1. A variable resistance element comprising a baseplate of insulating material, a first resistance film of low resistivity material on said baseplate and forming comblike electrodes of varying lengths, a second resistance film of varying width on said baseplate and electrically connected to the comblike electrodes formed by said first film, and a multicontact brush movable relative to said comblike electrodes and having a plurality of parallel contact fingers each engaging a different portion of each electrode, said contact fingers spanning four electrodes, at least two adjacent electrodes being engaged by said contact fingers; said contact fingers, extending transversely to the path of movement of said brush; said electrodes being arranged obliquely to the path of movement of said brush.
 2. A variable resistance element according to claim 1, wherein the path of movement of the multicontact brush is arcuate.
 3. A variable resistance element according to claim 1, wherein three consecutive contact fingers span two adjacent electrodes. 